1. Field of the Invention
The present invention relates to a test device for determining the presence of a constituent in a sample. The invention as defined by the claims comprises a test device, and a method for preparing it, in which potentially incompatible reactants are kept separate from each other until the actual testing of a sample, such as bodily fluid, takes place. Hence, the device comprises a carrier matrix incorporated with at least two reactants capable of interacting with a sample constituent being analyzed to produce a detectable response. The reactants are positioned separate from each other in substantially discrete, non-contacting areas on the carrier matrix.
2. Description of the Prior Art
The burgeoning field of test devices in the form of test strips has provided convenient and rapid analysis of various types of samples, including samples of biological, industrial, and automotive fluids, and the like. Diagnostic devices designed for detecting various clinically significant substances or constituents in biological fluids, such as urine and blood, including lysed or unlysed blood, blood plasma, and blood serum, have in many cases supplanted prior wet chemistry techniques which were both cumbersome and time-consuming. These diagnostic devices have thus assisted in the fast and accurate diagnosis and treatment of disease.
Conventional test strips generally comprise an absorbent or porous matrix incorporated with indicator reactants, usually of a colorimetric type. The sample to be tested is contacted with the matrix, such as by momentary immersion where the sample is liquid, and the indicator response is observed after a set period of time. For example, in a reagent strip for the detection of occult blood in urine a diagnostic strip can be employed which comprises an absorbent paper impregnated with o-tolidine and a peroxide. When this strip is wetted with urine containing occult blood, decomposition of the peroxide occurs with the accompanying oxidation of the o-tolidine to produce a color response. This test is sensitive and extremely useful in diagnosing urinary tract disorders. However, because of the relative incompatibility of employed reactants, shelf life has often been found to be relatively short and the strips can lose their sensitivity after long periods of storage.
Similar problems of reactant incompatibility occur in many other types of strips where more than one chemical reaction is involved. For example, reactants for testing ketone, blood urea nitrogen (BUN), and galactose levels have been known to have limited shelf lives. In order to explore ways of extending the shelf life of reagent test strips, i.e. methods of reducing the relative incompatibility of reactants, experiments were conducted to determine whether it would be possible to physically separate incompatible reagents on the strip itself. Prior to this work the successful separation of incompatible reagents had not been reported. The experiments were successful and it was found that reagent strips could indeed be prepared in which incompatible reactants were physically separated until becoming contacted with the sample to be analyzed. Strips prepared in accordance with the present invention have excellent shelf life and are vastly superior in this respect to present commercial strips containing the same reactants.